Nucleic acid-based biosensors have potential applications that range from genotyping to molecular diagnostics. Fluorescence-based techniques afford high-density nucleic acid arrays for analyzing specific nucleic acid sequences and gene expression. Although widely employed, these arrays require labeling of the target nucleic acid samples. Electrochemical transduction methods have therefore been proposed for ultrasensitive detection of nucleic acid hybridization events. The use of electrochemical techniques instead of fluorescence can allow for simpler and smaller detectors. The ability to directly detect nucleic acid selectively and sensitively has been a major goal of electrochemical research.